The present invention generally relates to a screen assembly and, more particularly, to a screen suspending and tilting mechanism for suspending the screen from above and also for tilting the screen relative to the direction of travel of image carrying rays of light from an optical projector.
The term "projector" hereinabove and hereinafter employed is to be understood as meaning an optical instrument including a slide projector, a motion picture projector, an overhead projector and any other image projecting device used for the purpose of reproducing an image, either still or motion, on the screen.
Various types of screen assemblies are now commercially available and a recent version of them is known to comprise a cylindrical casing, a four-sided sheet of predetermined size having at least one surface adapted to have an optical image projected thereon, a spindle coaxially rotatably housed within the cylindrical casing and to which one side portion of the screen sheet is secured while the side portion opposed to the one side portion of the screen sheet is situated outside the cylindrical casing, and a screen winder employed, for example, in the form of at least one coil spring. The coil spring has the opposite ends respectively secured to the cylindrical casing and the spindle and is arranged to operate in such a manner that, while the screen sheet is drawn out of the cylindrical casing by the application of an external pulling force against the coil spring which at this time accumulates a winding force, the screen sheet once drawn out of the cylindrical casing can automatically be drawn into the casing upon release of the external pulling force by the effect of the accumulated winding force of the coil spring.
With the conventional screen assembly, it has often been experienced that, when an optical image is projected on the screen surface with the optical axis of, for example, a slide projector directed at a certain angle relative to the screen surface, that is, when the screen surface receives the projected image at an angle of incidence more or less than 90.degree., the projected image is reproduced in perspective due to linear distortion. This linear distortion can readily be substantially corrected if the angle of incidence of rays of light carrying the projected image is adjusted or set to be substantially at right angles to the screen surface. Heretofore, this has been carried out by tilting the projector up or down or by lifting or lowering either the projector or the screen relative to the other.
However, depending upon the circumstances, the correction of the linear distortion occurring in the projected image or picture on the screen surface cannot be achieved whatever the method therefor may be, because each of the above described methods of distortion correction requires a complicated and time-consuming procedure and a lot of labor which, to the mind of on-lookers, appears to be exaggerated. described disadvantages and inconveniences, as disclosed in the Japanese Utility Model Publication (Unexamined) No. 67577/1974 laid open to public inspection on Dec. 22, 1975, I have invented a screen suspending and tilting mechanism. My prior screen suspending and tilting mechanism disclosed in the aforesaid publication comprises a screen assembly of any known construction having a screen sheet wound around a spindle within a screen casing, means for connecting the screen casing to an overhead supporting structure, for example, a ceiling of a room or hall, for rotation about an axis perpendicular to the plane of the overhead supporting structure and also to the longitudinal axis of the screen casing, and a tiltable support bar of telescopically extendable construction having a straight tube and a straight extension inserted in said straight tube for axial movement between retracted and projected positions. The means for connecting the screen casing to the overhead supporting structure includes a L-shaped bracket having a first flat portion, rotatably connected to the overhead supporting structure, and a second flat portion supporting the sereen casing therebelow by means of a pair of suspending bars and to which one end of the straight tube remote from the straight extension is pivotally connected by way of an angle member. A free end of the straight extension remote from the straight tube has a fixture rigidly mounted thereon, to which fixture one side portion of the screen sheet situated outside the screen casing is, after the screen sheet has been drawn out of the casing, engaged in readiness for receiving the projected image or picture thereon. At this time, depending upon the size of the area of the screen sheet which is desired to have the picture projected thereon, the straight extension may be set either to the retracted position, or to the projected position or to a position intermediate the retracted and projected positions.
The tiltable support bar can be pivoted from a vertically oriented position selectively to any one of a plurality of tilted positions for adjustment of the angle of the screen sheet relative to the direction of travel of a beam of light from the projector. For this purpose, my prior screen suspending and tilting mechanism further comprises a tilt angle adjusting mechanism for selectively positioning the tiltable support bar to any one of the tilted positions. The tilt angle adjusting mechanism is constituted by an angular slot defined in the angle member and a stop which is in the form of a bolt and a nut, the bolt being inserted through the angular slot with the angle member situated between a head portion of the bolt and the nut fastened to said bolt. Since a portion adjacent the end of the straight tube, which is pivotally connected to the angle member and situated remote from the extension, of the tiltable support bar tending to assume a vertically downwardly oriented position under the influence of gravity force acting on said tiltable support bar, is engaged with the stop, adjustment of the position of the bolt relative to the angular slot results in positioning of the tiltable support bar to a selected one of the tilted positions and, consequently, the screen is swung backwards substantially around the screen casing.
My prior screen suspending and tilting mechanism of the construction described above has been developed on the basis of the fact, where the projector, for example, an overhead projector, cannot be tilted up or down and/or cannot be lifted or lowered relative to the screen during an attempt to correct the linear distortion occurring in the projected picture, the only way to correct it is to tilt the screen. With the above described screen suspending and tilting mechanism, tilting of the screen sheet can readily be achieved merely by positioning the tiltable support bar to any selected one of the tilted positions since that side portion of the screen sheet remote from the screen casing is engaged with the fixture on the tiltable support bar with said screen held in a position drawn out of the screen casing.
Although my prior screen suspending and tilting mechanism operates satisfactorily and conveniently, some disadvantages have been found which are attributable to the position and construction of the tilt angle adjusting mechanism. By way of example, since the bolt and the nut, which constitute the tilt angle adjusting mechanism, are positioned adjacent the overhead supporting structure and spaced a greater distance from the ground or floor than the largest possible height of the user of the screen assembly, frequent adjustment of the tilt angle of the screen sheet to suit to a particular situation in which the screen and the projector are placed is often hampered.
In addition thereto, after the screen sheet once drawn out of the screen casing has been retracted into the screen casing and even though the straight extension of the tiltable supporting bar is retracted into the straight tube, a substantial length of the straight tube remains suspended in the air within the room or hall, tending to provide an obstruction which would impair the appearance of the room or hall.